I think the big win is that TeaVM has a lighter runtime and conditionally compiles only what is needed into the final JavaScript. There are tools that let Java

I think the big win is that TeaVM has a lighter runtime and conditionally compiles only what is needed into the final JavaScript. There are tools that let Java do this now, but I think the standard runtime has more cross dependencies. My app cross compiles to JVM and browser easily now, but I did a lot of work on the SnapKit UI framework, which is like Swing but abstracts out graphics and user input. My app used to be all Swing - that would be almost impossible with TeaVM. There is product called CheerpJ which does Swing with almost no modification, but it has a larger runtime.